HYPOTENSION IN AN UNINTENTIONAL OVERDOSE WITH TIZANIDINE

Background: Tizanidine, an imidazoline with central [[Alpha].sub.2] adrenergic agonist properties, is used to treat spasticity from spinal cord injuries. Although hypotension and bradycardia are adverse effects occasionally described in therapeutic doses, overdose data are limited. We report a case of severe hypotension following an unintentional overdosage of tizanidine. Case Report: A 47-year-old woman with spastic paraplegia secondary to sarcoidosis mistakenly took four (4 mg) tablets of tizanidine rather than her usual dose of one (4 mg) tablet and presented to the hospital within 15 minutes of her ingestion. On arrival, she was drowsy with the following vital signs: blood pressure, 107/69 mmHg; pulse, 86/min; respirations, 16/min; temperature, 97.4 [degrees] F; [O.sub.2] saturation 100%. Her physical examination was remarkable only for pinpoint pupils. An electrocardiogram showed a normal sinus rhythm and was otherwise unremarkable. Activated charcoal with sorbitol was administered and a crystalloid infusion was started at 150 mL/hour. About 3 hours post ingestion; she became hypotensive to a blood pressure of 74/48 mmHg. There were no mental status changes or other clinical symptoms associated with the hypotension. The crystalloid infusion was increased, and her blood pressure normalized after 4 L of normal saline. She was observed in an intensive care unit overnight with no further episodes of hypotension. Her vital signs the next day were: pulse, 70/min; blood pressure, 130/80 mmHg; respirations 12/ min; temperature, 98.8 [degrees] F. She was restarted on her normal doses of antispasticity medications including tizanidine and discharged home. Conclusions: Centrally acting [[Alpha].sub.2] adrenergic agonists are known to cause lethargy, hypotension and bradycardia. Interestingly, this patient was also mildly hypothermic, which is described with centrally acting [Alpha] adrenergic agonists. Clinical trials of tizanidine reported that the most common side effects were fatigue, dizziness, muscular weakness, and dry mouth. Hypotension occurred only occasionally and was altogether absent in some trials. There has only been one previously reported overdose case, and the patient developed hypotension with sino-atrial and atrio-ventricular node dysfunction. Although tizanidine may be well tolerated in therapeutic dosages, this case illustrates the potentially severe side effects from a small overdosage of tizanidine.
Chu J, Nelson LS, Hoffman RS. New York City Poison Control Center, New York City, New York, [...]